The present invention relates to a semiconductor device. More particularly, the present invention relates to a technology effectively applicable to a semiconductor device designed into a configuration of a multistage amplifier circuit.
A semiconductor device known as a high-frequency power amplifier (or a high-frequency power module) is incorporated in a portable communication apparatus such as a portable telephone or an car telephone of the PDC (Personal Digital Cellular) system or a portable telephone of the PHS (Personal Handyphone System). This high-frequency power amplifier is designed into a configuration of a multistage amplifier circuit in which a plurality of amplifying means are electrically connected to each other to form a multistage structure.
The high-frequency power amplifier is built by mounting a semiconductor chip on a main surface of a wiring substrate.
The semiconductor chip has an amplifying means formed on a main surface thereof. Electrodes formed on a main surface of the semiconductor chip are electrically connected to electrodes formed on a main surface of the wiring substrate by conductive wires. The amplifying means has a configuration in which typically a plurality of field-effect transistors are electrically connected to each other to form a parallel circuit. A gate terminal (serving as the input unit) of the amplifying means is electrically connected to a chip-side input electrode formed on the main surface of the semiconductor chip. On the other hand, a drain terminal (serving as the output unit) of the amplifying means is electrically connected to a chip-side output electrode formed on the main surface of the semiconductor chip. The chip-side input electrode is placed at a position on a particular side of the semiconductor chip whereas the chip-side output electrode is placed at a position on another side of the semiconductor chip facing the particular side. A source terminal of the amplifying means is electrically connected to a back-surface electrode formed on a back surface of another semiconductor chip facing the main surface. The back-surface electrode is fixed at a reference electric potential. The chip-side input electrode is electrically connected to a substrate-side input electrode formed on the main surface of the wiring substrate by an input wire. The substrate-side input electrode is placed at a position facing the particular side of the semiconductor chip cited above. The chip-side output electrode is electrically connected to a substrate-side output electrode formed on the main surface of the wiring substrate by an output wire. The substrate-side output electrode is placed at a position facing the other side of the semiconductor chip cited above.
By the way, in order to reduce the size and the cost of the high-frequency power amplifier, an attempt has been made to form a plurality of amplifying means on one semiconductor chip. In the case of two amplifying means formed on one semiconductor chip, for example, the amplifying means at the front stage is oriented in a direction opposite to a direction in which the amplifying means at the rear stage is oriented so that the input and the output of the amplifying means at the front stage are placed at locations in close proximity to respectively the output and the input of the amplifying means at the rear stage. As a result, the input and output wires at the front stage and the output and input wires at the rear stage are close to each other. As a result, there is raised a problem of a deteriorating high-frequency characteristic due to a mutual-induction effect between the input and output wires. In particular, the mutual-induction effect between the input wire of the front stage and the output wire of the rear stage is a serious problem since a difference between a power flowing through the input wire and a power flowing through the output wire is big.
A technology to prevent the high-frequency characteristic from deteriorating due to a mutual-induction effect between wires is disclosed for example in Japanese Patent Laid-open No. Hei 9-260412 (1997). According to this technology, a chip-side bonding electrode is formed between the chip-side input electrode and the chip-side output electrode whereas a substrate-side bonding electrode is formed between the substrate-side input electrode and the substrate-side output electrode. The chip-side bonding electrode is electrically connected to the substrate-side bonding electrode and, by fixing the chip-side bonding electrode and the substrate-side bonding electrode at a reference electric potential, the high-frequency characteristic can be prevented from deteriorating due to a mutual-induction effect between the input and output wires.
In addition, the high-frequency power amplifier module employing transistors is a key device of a portable telephone of mobile communication adopting systems such as the PDC (Personal Digital Cellular) system and the GSM (Global System for Mobile communication). The demand for such a portable telephone has been growing tremendously in recent years. Specifications of such a high-frequency power amplifier include a small size and a low cost in addition to good high-frequency characteristics for applications to mobile communication systems.
A technique to respond to such a demand is disclosed in Japanese Patent Laid-open No. 2755250. By placing 2 transistors, namely, a first-stage transistor 2000 and a second-stage transistor 3000, at locations close to each other on a semiconductor chip 1000 as shown in a top-view diagram of FIG. 21 and a squint-view diagram of FIG. 22, the size and the cost can be reduced. A bonding input electrode 2000b of the first-stage transistor 2000 is electrically connected to a bonding electrode 7000d of a wiring substrate 6000 by an input bonding wire 9000d. A bonding output electrode 3000c of the second-stage transistor 3000 is electrically connected to a bonding electrode 7000a of the wiring substrate 6000 by an output bonding wire 9000a. A bonding electrode 10000a on the semiconductor chip 1000 is electrically connected to a bonding electrode 12000a of the wiring substrate 6000 by a shield bonding wire 13000a. The shield bonding wire 13000a is provided between the input bonding wire 9000d and the output bonding wire 9000a. The bonding electrode 10000a and the bonding electrode 12000a at the ends of the shield bonding wire 13000a are connected to the ground at high frequencies by via holes bored through the semiconductor chip 1000 and the wiring substrate. It should be noted that the via holes themselves are not shown in the figure. By providing a shield bonding wire 13000a, the amount of coupling through a mutual inductance between the input bonding wire 9000d and the output bonding wire 9000a can be reduced, allowing the degree of deterioration of isolation between the high-frequency input and output terminals to be lowered. As a result, the high-frequency characteristic is improved.
The problem of coupling through a mutual inductance between the input bonding wire 9000d and the output bonding wire 9000a is raised by a location of the input of the first-stage transistor 2000 in close proximity to a location of the output of the second-stage transistor 3000 and a location of the output of the first-stage transistor 2000 in close proximity to the location of the input of the second-stage transistor 3000 which are caused by the fact that the first-stage transistor 2000 and the second-stage transistor 3000 are oriented in directions opposite to each other. In particular, the mutual-induction effect between the input bonding wire 9000d of the first-stage transistor 2000 and the output bonding wire 9000a of the second-stage transistor 3000 is a serious problem. This is because the high-frequency power output by the second-stage transistor 3000 is higher than the high-frequency power input to the first-stage transistor 2000 by 20 to 30 dB (or 100 to 1,000 times), giving rise to a positive feedback from the output to the input. Even though the output bonding wire 9000c of the first-stage transistor 2000 and the input bonding wire 9000b of the second-stage transistor 3000 are also close to each other, the problem of a deteriorating high -frequency characteristic caused by a mutual-induction effect does not arise due to the fact that a ratio of a high-frequency power flowing through the input bonding wire 9000b to a high-frequency power flowing through the output bonding wire 9000c is not greater than 0 dB (1 time).
In FIGS. 21 and 22, reference numerals 2000a and 3000a denote the main bodies of the first-stage transistor 2000 and the second-stage transistor 3000 respectively. Reference numerals 2000d and 3000d denote the source electrodes of the first-stage transistor 2000 and the second-stage transistor 3000 respectively. Reference numeral 2000c denotes the bonding output electrode of the first-stage transistor 2000 and reference numeral 3000b denotes the bonding input electrode of the second-stage transistor 3000. Reference numeral 4000 denotes a ground electrode whereas reference numerals 7000b and 7000c each denote a bonding electrode of the wiring substrate 6000. Reference numerals 8000a to 8000d each denote a lead electrode and reference numeral 104 denotes a cavity.
As a result of a study of the technology described above, however, the inventors of the present invention identified the following problems.
The substrate-side bonding electrode is placed between the substrate-side input electrode and the substrate-side output electrode. That is, the substrate-side input electrode, the substrate-side bonding electrode and the substrate-side output electrode are laid out along a straight line beside a side of the semiconductor chip.
In general, the substrate-side electrode is formed by adopting a screen printing technique. Thus, the area occupied by the substrate-side electrode is larger than the chip-side electrode which is formed by adopting a photolithography technique. In addition, a through-hole wire is formed right below the substrate-side electrode in order to make the propagation path short. Since the area of the through-hole wire in the plane direction (that is, the external size) has to be increased to a certain degree in order to give a low resistance, the area occupied by the substrate-side electrode becomes larger. Thus, when the substrate-side input electrode, the substrate-side bonding electrode and the substrate-side output electrode are laid out along a straight line beside a side of the semiconductor chip, the array of these electrodes is long. As a result, the chip-side input electrode and the substrate-side input electrode do not face each other anymore and, at the same time, the chip-side output electrode and the substrate-side output electrode also do not face each other as well. For this reason, the input and output wires become longer. When the input and output wires become longer, the inductance increases, causing the high-frequency characteristic to deteriorate. As a consequence, the gap between the amplifying means at the front stage and the amplifying means at the rear stage needs to be widened to make the input and output wires shorter. In this case, however, the area occupied by the semiconductor chip increases, giving rise to a hindrance to miniaturization of the high-frequency power amplifier.
An effect of the shield bonding wire 13000a of the conventional technology described above is explained by referring to FIG. 15. FIG. 15 is a diagram showing computed values of a coupling coefficient (or the mutual inductance expressed in terms of nH) between parallel input and output bonding wires of an amplifier. The 2 bonding wires each have a length of 1 mm (which is close to the real thing) and have bonding portions separated from each other by a distance d. A dotted line representing a coupling coefficient of 0.12 shows that the amplifier operates in a stable state for a coupling coefficient of 0.12 or smaller. The value 0.12 is found from FIG. 16 which shows a relation between the coupling coefficient and a coefficient of stability of the amplifier. The amplifier operates in a stable state for a coefficient of stability of at least 1. The bonding distance d cited above is defined as a distance between the centers of the bonding portions of the 2 bonding wires which are closest to each other.
FIG. 15 indicates that the conventional technology taking a countermeasure of providing shield bonding wires results in small coupling coefficients in comparison with a case with no shield bonding wires (which is denoted by a phrase xe2x80x98No countermeasurexe2x80x99 in the figure) and, hence, exhibits an improved high-frequency characteristic. In addition, for coupling coefficients not exceeding 0.12, the countermeasure allows a wider range of the distance d between bonding portions, raising the degree of design freedom. Moreover, the distance d between bonding portions can be decreased to 0.55 mm, allowing the chip area to be made smaller. As a result, the module can be made small in size and the cost can be reduced.
In actuality, however, since the inductance of a via hole is added in series to each end of the shield bonding wire 13000a, a sufficient improvement of the high-frequency characteristic can not be achieved by the conventional technology
It is thus an object of the present invention to provide a technology that is capable of making a semiconductor device small in size.
To be more specific, it is an object of the present invention to provide a high-frequency power amplifier module that is capable of further improving the high-frequency characteristic thereof.
The present invention as well as other objects and novel characteristics thereof will become more apparent from the description of this specification and accompanying diagrams.
An outline of a representative of the present invention disclosed in this patent application is described briefly as follows.
A semiconductor device comprises: a semiconductor chip having a square surface; a wiring substrate having a main surface thereof used for mounting the semiconductor chip; a first electrode formed on a first area of a main surface of the semiconductor chip and placed at a location in close proximity to a side of the semiconductor chip; first amplifying means formed on the first area of the main surface of the semiconductor chip and provided with an input unit electrically connected to the first electrode; a second electrode formed on a second area of the main surface of the semiconductor chip and placed at a location in close proximity to the side of the semiconductor chip; second amplifying means formed on the second area of the main surface of the semiconductor chip and provided with an output unit electrically connected to the second electrode; a third electrode formed on a third area between the first and second areas of the main surface of the semiconductor chip; a fourth electrode formed on the main surface of the wiring substrate to face the side of the semiconductor chip and electrically connected to the first electrode by a first wire; a fifth electrode formed on the main surface of the wiring substrate to face the side of the semiconductor chip and electrically connected to the second electrode by a second wire; and a sixth electrode formed on the main surface of the wiring substrate to face the side of the semiconductor chip and electrically connected to the third electrode by a third wire with an electric potential thereof fixed at a reference level,
wherein:
the sixth electrode is placed at a location farther from the side of the semiconductor chip than the fifth electrode; and
the fourth electrode is placed at a distance from the side of the semiconductor chip about equal to a distance of the fifth electrode from the side of the semiconductor chip or at a location farther from the side of the semiconductor chip than the sixth electrode.
Since a gap between the fourth and fifth electrodes in the semiconductor chip described above can be narrowed by an amount corresponding to the size of an area occupied by the sixth electrode, a gap between the first and second areas can also be made narrow as well. As a result, since the area occupied by the semiconductor chip can be shrunk, the semiconductor chip can also be made small in size.
In addition, the objects described above can be achieved by a high-frequency power amplifier module having a semiconductor chip thereof provided on a wiring substrate having a base thereof made of a dielectric material. The high-frequency power amplifier module is designed into a configuration wherein: amplifying transistors of two or more stages, a bonding input electrode for inputting a high-frequency power to the amplifying transistors and a bonding output electrode for outputting a high-frequency power from the amplifying transistors are provided on the semiconductor chip; an angle formed by a first auxiliary line connecting bonding portions to each other at the two ends of an input bonding wire connecting the bonding input electrode for a specific one of the amplifying transistors to the wiring substrate and a second auxiliary line connecting bonding portions (their centers) to each other at the two ends of an output bonding wire connecting the bonding output electrode for another amplifying transistor at a stage following the specific amplifying transistor to the wiring substrate is in the range 72 degrees to 180 degrees; and a gap between bonding portions of the bonding input electrode and the bonding output electrode is at least 0.3 mm but smaller than 0.8 mm.
In spite of the condition stipulating that the gap between bonding portions of the bonding input electrode and the bonding output electrode is at least 0.3 mm but smaller than 0.8 mm, the above objects can be achieved provided that the high-frequency power amplifier module is designed to give a coefficient of stability of at least one between the two amplifying transistors.